Device and method for providing a selective heat treatment on a metal sheet

ABSTRACT

A device for providing selective heat treatment on a metal sheet comprising boron steel is provided. The device comprises a laser source for emitting a laser beam onto the metal sheet to provide a selective heat treatment thereon, wherein a defined heat treated grid pattern is formed on the metal sheet by the selective heat treatment. The device further comprises a control unit arranged to control the operation of the laser source for providing the defined heat treated pattern onto the metal sheet; and control the case hardness depth of the defined heat treated pattern based on a temperature parameter and a holding time parameter associated with the operation of the laser source. A method for performing controlling the case hardness depth of a selectively heat treated metal sheet of boron steel is also provided.

TECHNICAL FIELD

The current disclosure relates to the field of selective heat treatment of sheet metal materials. More specifically it relates to the control of the case hardness depth resulting from the selective heat treatment.

BACKGROUND

In order to increase stability and endurance of a metal sheet it may be subjected to what is known as press hardening. Press hardening processes allow for the production of light weight, high strength metal sheet components. Press hardened materials are highly deformation resistant. Press hardening techniques have played an increasingly important role within the vehicle industry during recent years, as the press hardened components are suitable for absorbing great deformation energies such as in a vehicle collision. In current press hardening processes the metal sheet is transported through a furnace and thus heated up to its austenization temperature of about 900 to 950° C. whereby it is transformed into 100% austenite. In the austenitic state the material has a tensile strength of about 200 MPa and an extension degree of about 40%. After the heat treatment the austenite material is rapidly moved into a processing tool for shaping the material before it starts to oxidize. Usually the duration of the shaping stage is about 8 to 10 seconds. During the shaping the shaped material is subject to cooling during which the austenite is transformed to marteniste. In other words a phase transformation occurs during the cooling. When the shaped material leaves the shaping tool, its temperature is about 150 to 200° C.

Press hardening however means that the entire sheet of metal will be hardened, which sometimes may not be desirable. It is also a non flexible process.

However, more flexibility in hardening the metal sheet is desirable.

Hence, there is a need for devices and methods which enable optimized and selective hardening of a metal sheet material e.g. based on material and the purpose of the finished product comprising the metal sheet.

SUMMARY

An object of the present invention is to eliminate or alleviate at least one of the drawbacks mentioned above, in accordance with the appended claims.

An advantage of the present invention is that a process of controlling the case hardness depth in a selective heat pattern provided on a metal sheet comprising boron steel is provided.

By being able to control the case hardness depth of the selective heat pattern the metal sheets may be tailor made in terms of formability, and deformation capability etc.

According to an aspect a device for providing selective heat treatment on a metal sheet comprising boron steel is provided. The device comprises a laser source for emitting a laser beam onto the metal sheet to provide a selective heat treatment thereon, wherein a defined heat treated pattern is formed on the metal sheet by the selective heat treatment. The device further comprises a control unit arranged to control the operation of the laser source for providing the defined heat treated pattern onto the metal sheet. Moreover, the control unit is arranged to control the case hardness depth of the defined heat treated pattern based on a temperature parameter and a holding time parameter associated with the operation of the laser source.

According to another aspect a method for providing a defined heat treated pattern on a metal sheet comprising boron steel is provided. The method comprises emitting a laser beam onto the metal sheet to provide the selective heat treatment thereon. Moreover, the method comprises controlling the operation of the laser source for providing the defined heat treated pattern onto the metal sheet. Furthermore, the method comprises controlling the case hardness depth of the defined heat treated pattern based on a temperature parameter and a holding time parameter associated with the operation of the laser source.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages will appear from the following detailed description of embodiments, with reference being made to the accompanying drawings, in which:

FIG. 1 is a schematic drawing showing a device for providing a selective heat treatment on a metal sheet;

FIG. 2 is a schematic drawing showing an alternative device for providing a selective heat treatment on a metal sheet;

FIG. 3 shows a block chart of a method;

FIG. 4 is a schematic drawing illustrating shaped metal sheet part being provided with a grid pattern before or after shaping;

FIG. 5 is a schematic drawing illustrating shaped metal sheet part being provided with a grid pattern;

FIG. 6 is a schematic drawing illustrating shaped metal sheet part being provided with a grid pattern before or after shaping;

FIGS. 7a and 7b show two examples of the ability of controlling the case hardness depth using a CO2 laser; and

FIGS. 8a and 8b show two examples of the ability of controlling the case hardness depth using a fiber laser.

DETAILED DESCRIPTION

An idea of the present invention is to controllably conduct selective heat treatment on the metal sheet based on the desired properties of a ready-to-use component formed by the metal sheet. The desired properties may relate to a desired metal sheet formability or trimability of the metal sheet and/or required in-use properties of the ready-to-use component comprising the selective heat treated metal sheet.

The selective heat treatment includes heating the sheet material according to a defined heat treatment pattern, forming a grid pattern, followed by cooling and thereby generating a grid pattern wherein the metal sheet is locally annealed or hardened compared to the non-treated portions of the metal sheet.

It is an aim of the present invention to provide a solution as how to control the hardening and/or annealing process, and in particular relating to the ability of controlling the case hardness depth in the areas associated with the defined heat treated pattern.

The inventors have realized that the selective heat treatment may be optimized for different applications by controlling the selective heat treatment such that a specific case hardness depth of in the metal sheet may be obtained.

The metal sheet may comprise boron steel. During the selective heat treatment, the boron steel along the lines of the specific heat pattern converts into austenite at elevated temperature (≥925° C.). During subsequent cooling, the austenite converts into martensite along the lines of the specific heat pattern. The martensite acts as a hardened or reinforcing structure of the metal sheet.

FIG. 1 illustrates a device 100 for providing a defined heat treated pattern on a metal sheet comprising boron steel. The device comprises a laser source 101 and a control unit 103 operatively connected to the laser source 101. The control unit has processing capabilities and may comprise a processor and memory.

Optionally, the device may comprise a movement device 105 arranged to move the metal sheet 104 in relation to the laser source 101. The movement device 105 may for example be a conveyer belt.

The selective heat treatment is performed by the laser source emitting a laser beam 102 onto a metal sheet 104 in the defined heat treated pattern.

The control unit 103 is arranged to control the operation of the laser source 101 for providing the defined heat treated pattern onto the metal sheet. Moreover, the control unit is further arranged to control the case hardness depth of the defined heat treated pattern based on a temperature parameter and a holding time parameter associated with the operation of the laser source 101.

By being able to control the case depth parameter the selectively heat treated metal sheet may be given tailor made formability and reinforcing properties. For example, while a smaller (in relation to the thickness of the metal sheet) case hardness depth provide for increased subsequent formability the abrasion resistance is reduced, whereas a larger case hardness depth provides for increased abrasion resistance at the expense of reduced subsequent formability properties.

The laser source 101 may for example be a carbon dioxide (CO₂) laser or a fiber laser.

The control unit 103 may control the case hardness depth based on input, e.g. in the form of an input signal, comprising information associated with a desired case hardness depth of the defined heat treated pattern to be applied to the metal sheet 104.

In some embodiments, the temperature parameter may define a temperature range for the case of the metal sheet during the selective heat treatment, e.g. ranging from the transition temperature of the metal sheet and up to just below the melting temperature of the metal sheet. It should be appreciated that the holding time when using a temperature closer to transition temperature is longer than that when using a temperature closer to the melting temperature.

For example, carbon and stainless steel have a phase transition temperature of about 925° C. and a melting temperature of about 1700° C.; aluminum has a transition temperature of about 200° C. and a melting temperature of about 400° C.; magnesium has a transition temperature of about 100° C. and a melting temperature of about 350° C. and titanium 925° C.

In order to improve the throughput of the selective heat treatment, a holding time as short as possible is normally preferred.

The device may optionally comprise a temperature sensor (not shown) for measuring the actual temperature in the defined heat treated pattern. The temperature sensor may be operatively connected to the control unit for providing the latter with present temperature measurements. The temperature sensor may be an infrared sensor, such as an infrared laser temperature sensor, being able to accurately measure the temperature in the defined heat treated pattern or adjacent areas remotely.

The temperature sensor may e.g. be placed adjacent to the laser source at a distance from the metal sheet, and measuring the temperature in a point along the defined heat treated pattern just behind the point of the metal sheet currently being irradiated by the laser beam 102 of the laser source 101.

The temperature sensor may be a thermal camera operatively connected to the control unit. The thermal camera, e.g. an IR camera, may be arranged to detect heat from both the grid lines of the grid pattern and the non-treated areas adjacently arranged the grid pattern.

Optionally, the control unit 103 may be configured to measure the depth of the case hardness of the metal sheet. If the depth of the case hardness is deemed to be too small for a desired application the control unit 103 may operate the laser such that the temperature is increased. For example, the depth of the case hardness may be measured using a camera imaging the edge of the metal sheet. The edge camera may be arranged to detect light in the visual light spectrum, i.e. in the wavelength range of 400 to 700 nm. By means of an edge detection camera grid lines extending to the edge of the metal sheet at an angle may be analyzed whereby the depth of the case hardness at the grid lines may be measured and be fed back to the control unit, which may adapt the operation parameters accordingly.

In order to increase the temperature for the remainder of the defined heat treated pattern, the power of the laser could be increased, e.g. by means of a control signal sent from the control unit to the laser source. Thus, the case hardness depth may also be controlled by varying the power of the laser and the laser speed or the speed of the sheet movement.

The temperatures to which the metal sheet may be elevated to in order to accomplish the phase change, formability, trimability, property change or improvement are e.g. in the range of 100 to 1700° C. depending on the material of the metal sheet.

In some embodiments, the control unit 103 may additionally or alternatively also control the holding time parameter, e.g. by controlling the laser speed or the speed of the sheet movement, in order to control the case hardness depth.

The holding parameter may determine a time period during which each metal sheet portion of the defined heat treated pattern is above a predefined temperature. The reason why a holding time needs to be considered is because it takes some time for the material of the metal sheet in the selectively heat treated region to completely convert into austenite. The process of converting the boron steel to austenite includes reforming the core and crystals of the material in terms of size and shape.

For example, in a commonly known process of heat treating whole metal sheets, i.e. where the entire metal sheet is to be converted into austenite, requires a holding time of at least 5 minutes. Hence, each metal sheet blank requires a holding time of at least 5 minutes.

An aim of the present invention is to reduce the holding time parameter as far as possible, and this is possible by conducting the selective heat treatment at temperatures higher than those required to initiate the material phase transformation but below the melting point of the metal sheet.

In general, the holding time parameter and the temperature parameter are related to the case hardness depth as follows. A lower temperature in the metal sheet, still above the minimum phase change temperature, will require a longer holding time than that of a higher temperature, in order to achieve the same case hardness depth of the metal sheet. Hence, for temperatures above the minimum phase change temperature, e.g. 950° C. for boron steel to convert into austenite, the temperature parameter and holding time parameter are inversely proportional to one another, in order to achieve the same case hardness depth

It should be appreciated that in order to control the case hardness depth, the temperature in the metal sheet achieved by the irradiating laser beam should never be at or above the melting point of the metal sheet. Hence, the control unit is arranged to control the operation of the laser source such that the metal sheet is never subjected to temperatures above the melting temperature of said metal sheet.

Calibration Mode

The control unit may operate in a calibration mode. In the calibration mode a series of grid lines having a certain length are formed in the metal sheet with different parameter settings. The parameters as well as the input from any temperature sensor, such as the heat camera, and/or the case hardness depth measuring camera are then stored into the memory of the control unit. The parameters may be stored in a calibration table. Based on receipt of a desired case hardness depth, the control unit may be arranged to select appropriate parameter values from the calibration table.

For example, the calibration may be executed by selectively heat treating grid lines having a length of just a few centimeters with a number of different parameter settings.

Optionally, the control unit may be arranged to extrapolate suitable parameter values from parameter values stored in the calibration table, e.g. when the specific desired case hardness depth is not present in the calibration table.

Selective Heat Treatment Mode

The control unit may also operate in a normal operation mode, or selective heat treatment mode, in which it controls the operation of the laser source in order to conduct the selective heat treatment of the metal sheet such that the resulting grid pattern meets a desired case hardness depth.

In the selective heat treatment mode the temperature sensor, e.g. the thermal camera, and/or the case hardness depth measuring camera, are used to provide continuous or intermittent feedback to the control unit, such that the desired case hardness depth is achieved and maintained throughout the selective heat treatment process.

The feedback loop from the temperature sensor and/or case hardness depth measurement sensor provides the control unit with a built-in treatment process monitoring functionality.

For example, based on input that the case hardness depth is too shallow or small the control unit 103 may be configured to control the laser source such that it illuminates the same spot of the metal sheet 104 for a longer period of time.

Alternatively or additionally, in the event the metal sheet 104 is provided on the conveyer belt 105, the control unit 103 may control the conveyor speed of the conveyer belt such that each part of the defined heat treated pattern of the metal sheet 104 is irradiated by the laser source 101 for a longer period of time. Hence, by slowing the conveyor speed down the longer each point of the metal sheet will be irradiated per time unit.

It should be noted that the laser source may be arranged to move over the metal sheet to provide the grid pattern thereon. Alternatively, or additionally the metal sheet may be moved in relation to the laser source by means of the aforementioned conveyor belt 105. Hence, in under some conditions both the laser source may move over the metal sheet while the conveyor belt moves the metal sheet.

Experiments have shown that is possible to controllably achieve a specific case hardness depth in the metal sheet independently of the laser beam incidence angle, i.e. the angle at which the laser beam hits the surface of the metal sheet. This finding makes the arrangement of the device, particularly when providing selective heat treatment on already formed or shaped metal sheets, significantly less complex.

The laser source 101 may in some embodiments be a carbon dioxide (CO₂) laser or a fiber laser.

The laser beam 102 may be set to a uniform distribution or a Gaussian distribution which is well known. A Gaussian distribution setting results in that the spot shape of the laser beam is circular, while for a uniform distribution the spot shape of the laser beam is square shaped. Experiments have showed that a Gaussian distribution setting may be preferred for some applications, see e.g. examples in relation to FIGS. 7a to 8b below. When using a Gaussian distribution the transition between the hardened grid line and the non-hardened adjacent areas is more smooth, compared to that resulting from a uniform distribution, which provides for an improved abrasion resistance and improved flexibility for subsequent forming of the metal sheet.

Although, a Gaussian distribution (circular spot shape) has shown to be preferred, depending on the application the control unit 103, upon receipt of the input signal, may be further arranged to control case hardness depth by adapting the circular laser focus spot shape to a square shaped spot shape.

In some applications, the selective heat treatment is conducted to improve the strength either before or after forming of the metal sheet.

The specific heat pattern, e.g. grid pattern, may be said to form a skeleton structure in the metal sheet. The grid pattern may improve or facilitate subsequent forming of the sheet material. A grid pattern or a portion of the grid pattern may also be designed to allow for tailor-made deformation capabilities of the resulting metal sheet component, see e.g. FIGS. 4 to 6.

The grid pattern, its shape and position in view of the metal sheet is designed and carried out based on the identified needs or requirements concerning forming, trimming and/or component performance or properties. Hence, the design of the grid pattern may be derived by reverse engineering through for instance crash simulation.

In case boron steel sheet is used, the sheet material along the lines of the grid pattern will convert into austenite during the heating process. Moreover, the selective heat treatment may comprise cooling the selectively heated sheet material, whereby the austenite along the lines of the grid pattern is converted into martensite. Here, the forming step may be executed immediately after the selective heat treatment, such that parts of the sheet material, in particular the martensite grid pattern, has a higher temperature than the ambient temperature.

The cooling may be induced by actively cooling the metal sheet, e.g. by an air cooling device.

Alternatively, the cooling is applied through the ambient or still air, such that a passive cooling at a sufficient rate of the defined heat treated pattern is achieved. The sufficient rate may be around 27° C. per second up to around 50° C. per second, since this is the known cooling rate required for the austenite to convert into martensite. In fact, the passive cooling, i.e. not using any cooling device, has shown to meet the sufficient cooling rate of 27° C. per second, since the selective heat treatment is local, meaning that the adjacent areas to the grid pattern are very cool, i.e. close to room temperature, in relation to the temperature of the grid pattern, thereby cooling the heated grid lines sufficiently rapid for the austenite to convert into martensite.

It is also possible to cool the heat treated metal sheet using by allowing the metal sheet to engage in relatively cooler objects, such as tools, dies and jigs/fixtures or cooled tools & dies, wherein the tools e.g. have heat exchanging channels filled with a refrigerant fluid flowing there through, and jigs/fixtures.

In order to apply the defined heat treated pattern to the metal sheet a plurality of laser sources could be utilized, as is illustrated in FIG. 2.

FIG. 2 illustrates an example embodiment of the device 200 for providing a selective heat treatment on the metal sheet.

The device 200 comprises two laser sources 201 a, 201 b connected to a control unit 203. During the selective heat treatment, the laser sources 201 a, 201 b emits a respective laser beam 202 a, 202 b onto a metal sheet 104 according to a defined heat treated pattern 205.

The laser sources 201 a, 201 b, the control unit 103 and the metal sheet 104 may e.g. be the same laser source, control unit and metal sheet as descried in conjunction with FIG. 1. The device 200 of FIG. 2 is illustrated without a conveyer belt, however it should be appreciated that the device 200 of FIG. 2 may also be connected to a conveyor belt in the same manner as in FIG. 1.

The laser sources 201 a, 201 b direct their respective laser beams 202 a, 202 b such that they form the grid pattern 205. Thus, only the metal sheet portions at the position of the grid pattern 205 will be heated and transform into martensite.

The first laser source 201 a irradiates the sheet material intermittently along a grid line extending over the width of the metal sheet 204 coil or blank (the expression “intermittently” is here meant to be understood as occurring at regular intervals). The second laser unit 201 b may be configured to provide at least one grid line in the longitudinal (i.e. parallel to the direction of movement indicated by the arrow) direction of the metal sheet 204. As can be seen in FIG. 2, although no conveyor is shown the relative movement between the laser sources and the metal sheet is shown by the dashed arrows.

In its simplest form, the grid shown in FIG. 2 can be applied by a single laser source, e.g. by the laser source as described in FIG. 1. In more advanced systems, the grid pattern can be created by a mirror-based pattern generator in laser systems.

The control unit 103 may be arranged to control the operation of the laser source(s) 201 a, 201 b for providing a defined heat treated pattern onto the metal sheet and to further control the case hardness depth of the defined heat treated pattern based on a temperature parameter and a holding time parameter associated with the operation of the laser source, wherein the laser speed, i.e. the speed at which the laser beam travels over the metal sheet, or the sheet movement speed is associated with both of these said parameters. The holding time may be reduced by increasing the relative speed between the laser source and the metal sheet. This relative speed may be increased by either increasing the laser speed or the metal sheet speed or both. Moreover, the shorter time period during which the laser beam hits a certain point on the metal sheet the lower the temperature increase in said point will be. Hence, the relative speed between the laser beam and the metal sheet also affects the temperature of the heat pattern.

The control unit 103 may control the case hardness depth based on receipt of an input signal comprising information associated with a desired case hardness depth of the defined heat treated pattern applied to the metal sheet 104.

FIG. 3 illustrates a method 300 for according to some embodiments. The method 300 comprises controlling 301 the operation of a laser source emitting a laser beam (e.g. any of the laser beams as described in conjunction with FIGS. 1 and 2) onto a metal sheet (e.g. any of the metal sheets as described in conjunction with FIGS. 1 and 2) to provide a defined heat treated pattern thereon. The metal sheet may e.g. comprise boron steel.

The method further comprises controlling 302 the case hardness depth of the defined heat treated pattern based on a temperature parameter and a holding time parameter associated with the operation of the laser source.

The method 300 may further comprise monitoring 303 the case hardness depth to check whether it differs from a predetermined level.

If it in 303 is determined that the case hardness depth is below the depth threshold (yes path out of 303) it is an indication that the depth needs to be increased and the method continues to 304 where at least one of a holding parameter or a temperature parameter is increased.

Thus, either the temperature of the laser beam is increased, e.g. by increasing the power of the laser, and/or the holding time during which the grid pattern applied to the metal sheet is subjected to the laser beam is increased resulting in that the case hardness depth is increased. In general, it is more preferred to keep the holding time to a minimum while adapting the temperature to achieve the desired case hardness depth.

If it in 303 is determined that the case hardness depth is above, or on, the depth threshold (no-path out of 303) then, that is a indication that the depth should not be increased further and the method continues to 305 where at least one of the temperature parameter or the holding time parameter is decreased.

The method then returns to 303 where the case depth hardness is monitored.

In some embodiments, step 303 of the method 300 may comprise determining the case hardness depth based on receipt of an input signal comprising information associated with a desired case hardness depth of the defined heat treated pattern. Optionally, the input signal may be created by a user typing in a desired case hardness depth using a user interface operatively connected to the control unit.

In some embodiments, the method may further comprise, upon receipt of said input signal, controlling the depth of the case of the metal sheet by adapting the power of the laser source such as to result in a grid pattern temperature ranging between the transition temperature and up to just below the melting temperature of the metal sheet. For example, an increase in the power of the laser source results in a stronger laser beam which results in a deeper case depth.

The temperature parameter may determine a temperature range for the case of the metal sheet during the selective heat treatment.

The holding time parameter may determine a time period during which each metal sheet portion of the defined heat treated pattern is above a predefined temperature. The laser speed and/or the sheet movement speed and the accomplished temperature control the holding time.

The method may further comprise controlling the case hardness depth by adapting the laser beam incidence angle onto the metal sheet.

The laser beam has a circular spot shape.

The method may further comprise controlling the case hardness depth by adapting the circular laser focus such that a variable laser spot size is achieved.

The laser source is a carbon dioxide laser or a fiber laser.

The selective heat treatment is applied to a first surface of the metal sheet, which first surface is selected to coincide with an outer surface after forming or shaping the metal sheet.

In case the purpose of the selective heat treatment is to improve the formability or trimability, the grid pattern must be applied before forming or trimming. For the application that the formability and trimability of the metal sheet is to be improved, the metal sheet is selectively heated up to a temperature below the transition temperature. In this way the metal sheet is not hardened but instead annealed.

FIGS. 4 to 6 each illustrates different applications where a grid pattern has been applied to a metal sheet which then has been formed or shaped into a finished part.

Turning to FIG. 5, the grid pattern shown may be produced by a laser source arranged on a robotic arm allowing the laser source to move relative to the flat metal sheet or the formed metal sheet.

FIGS. 7a and 7b show two comparable cross-sectional micrographs examples of the ability of controlling the case hardness depth of a 1.0 mm thick boron steel Boloc02 metal sheet. A CO₂ laser unit is used. The purpose of the selective laser heat treatment is to reinforce the sheet material strength. The selective heat treatment was conducted on a flat (undeformed) metal sheet. Laser spot shape and size is 6.24 mm, and the sheet is heated to 950° C., after which it is allowed to be still air-cooled.

Practical Examples

FIGS. 7a to 8b show a number of practical examples where a Gaussian distribution, i.e. circular spot laser beam shape, has been used for the selective heat treatment.

In FIG. 7a , the laser power is 650 W and the scan speed is 500 mm/min resulting in a hardness depth of 0.6 mm. In FIG. 7b , the laser power is 2300 W and the scan speed is 5000 mm/min and the resulting hardening depth is 0.17 mm. In both cases, the initial sheet hardness is 220 HV and the hardness in the hardened region is 470 HV.

The information shown in FIGS. 7a and 7b is of great importance. It exemplifies the optimization of the laser heat treatment process in order to achieve the wanted impacts on the selectively laser heat treated component. It also shows the possibility and opportunity to generate variety depending on the needs and one has therefore access to more parameters to accomplish the varying properties in different part locations.

FIGS. 8a and 8b show two comparable examples of the ability of controlling the case hardness depth using a fiber laser as laser source. The metal sheet is still a 1 mm thick boron steel Boloc02 graphitized for better coupling. The laser spot shape and size is 5.5 mm in both cases. The laser effect/power is 670 W in both FIGS. 8a and 8b . The laser (scan) speed is however, 1320 mm/min and 1500 mm/min respectively. Argon protection gas is used in both cases. The case hardness depth is 0.9 mm in FIG. 8a , while it is 0.45 mm in FIG. 8b . The initial hardness is 220 HV. It is increased to 490 HV in the hardened region in FIGS. 8a and 470 in the hardened region in FIG. 8 b.

It is possible to accomplish the same results as in FIG. 8a by using other laser processing parameters. Temperature control, e.g. 1500° C. in the metal sheet and 25 mm/sec in laser speed, yields the same results as in FIG. 8a . In other words, the heat treatment parameters can be selected differently as long the results are in compliance with those wanted.

Reference has been made herein to various embodiments. However, a person skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the claims. For example, the method embodiments described herein describes example methods through method steps being performed in a certain order. However, it is recognized that these sequences of events may take place in another order without departing from the scope of the claims. Furthermore, some method steps may be performed in parallel even though they have been described as being performed in sequence.

In the same manner, it should be noted that in the description of embodiments, the partition of functional blocks into particular units is by no means limiting. Contrarily, these partitions are merely examples. Functional blocks described herein as one unit may be split into two or more units. In the same manner, functional blocks that are described herein as being implemented as two or more units may be implemented as a single unit without departing from the scope of the claims.

Hence, it should be understood that the details of the described embodiments are merely for illustrative purpose and by no means limiting. Instead, all variations that fall within the range of the claims are intended to be embraced therein. 

1. A device for providing selective heat treatment on a metal sheet comprising boron steel, comprising a laser source for emitting a laser beam onto the metal sheet to provide a selective heat treatment thereon, wherein a defined heat treated pattern is formed on the metal sheet by the selective heat treatment; and a control unit arranged to: control the operation of the laser source for providing the defined heat treated pattern onto the metal; and control the case hardness depth of the defined heat treated pattern based on a temperature parameter and a holding time parameter associated with the operation of the laser source.
 2. The device according to claim 1, wherein the control unit is further arranged to control the case hardness depth based on receipt of an input signal comprising information associated with a desired case hardness depth of the defined heat treated pattern.
 3. The device according to claim 2, wherein the control unit, upon receipt of said input signal, is arranged to adapt at least one of the temperature parameter or the holding time parameter by adapting the laser speed or sheet movement speed.
 4. The device according to claim 1, wherein the control unit, upon receipt of said input signal, is further arranged to control the depth of the case of the metal sheet by adapting the power of the laser source.
 5. The device according to claim 1, wherein the temperature parameter determines a temperature range for the treated metal sheet grid pattern during the selective heat treatment.
 6. The device according to claim 1, wherein the holding time parameter determines a time period during which each metal sheet portion of the defined heat treated pattern is above a predefined temperature.
 7. The device according to claim 1, wherein the selective heat treatment is applied to a first surface of the metal sheet, which first surface is selected to coincide with an inner surface after forming or shaping the metal sheet.
 8. The device according to claim 1, wherein the temperature parameter relates to a temperature value range between a transition temperature for the metal sheet and below a melting temperature of the metal sheet.
 9. The device according to claim 1, wherein the laser beam has a circular spot shape resulting from a Gaussian distribution setting on the laser source.
 10. The device according to claim 9, wherein the control unit, upon receipt of the input signal, is further arranged to control case hardness depth by adapting the circular laser focus to a square shaped laser beam spot shape by selecting a uniform distribution setting for the laser source.
 11. The device according to claim 1, wherein the laser source is a carbon dioxide laser or a fiber laser.
 12. A method for providing a defined heat treated pattern on a metal sheet comprising boron steel, the method comprising emitting a laser beam onto the metal sheet to provide the selective heat treatment thereon; controlling the operation of the laser source for providing the defined heat treated pattern onto the metal sheet; and controlling the case hardness depth of the defined heat treated pattern based on a temperature parameter and a holding time parameter associated with the operation of the laser source.
 13. The method according to claim 12, further comprising controlling the case hardness depth based on receipt of an input signal comprising information associated with a desired case hardness depth of the defined heat treated pattern.
 14. The method according to claim 13, further comprising, upon receipt of said input signal, adapting at least one of the temperature parameter or the holding time parameter by adapting the laser speed and/or the sheet metal movement speed.
 15. The method according to claim 12, further comprising, upon receipt of said input signal, controlling the depth of the case of the metal sheet by adapting the power of the laser source.
 16. The method according to claim 12, wherein the temperature parameter determines a temperature range for the treated metal sheet grid pattern during the selective heat treatment.
 17. The method according to claim 12, wherein the holding time parameter determines a time period during which each metal sheet portion of the defined heat treated pattern is above a predefined temperature.
 18. The method according to claim 12, wherein the selective heat treatment is applied to a first surface of the metal sheet, which first surface is selected to coincide with an inner surface after forming or shaping the metal sheet.
 19. The method according to claim 12, wherein the laser beam has a circular spot shape resulting from a Gaussian distribution setting on the laser source.
 20. The method according to claim 19, wherein the control unit, upon receipt of the input signal, further controls the case hardness depth by adapting the circular laser focus to a square shaped laser beam spot shape by selecting a uniform distribution setting for the laser source.
 21. The method according to claim 12, wherein the laser source is a carbon dioxide laser or a fiber laser. 